Lubricated discharge orifice for restraining plastic flow

ABSTRACT

A lubricating layer is fixed on the wall of the discharge orifice of a continuous internal mixer of the kind wherein the internal pressure of the material being mixed in controlled by the choking effect of this orifice on the material discharged therethrough whenever new material us fed into the mixer. This provides a smoother restraint of the discharging material and therefore more uniform control of the pressure on the material while it is in the mixer.

Feb' 9 1,971 f Y R. -ncomss ETAL' 3,561,045

fLulfIcATEn DISCHARGE ORIFICE FOR RESTRAINING PLASTIC FLow med march 5, 196s 'li L 2V V INVENTORS @cf/ARD /Y COMES By h/AL r6? ,4. /Q/Ofnsk/ /4 ONEXS United States Patent O 3,561,046 LUBRICATED DISCHARGE ORIFICE FOR RESTRAINING PLASTIC FLOW Richard N. Comes, Woodbridge, and Walter A. Rapetski, Orange, Conn., assignors, by mesne assignments, to `USM Corporation, Boston, Mass., a corporation of New erse y Filed Mar. 5, 1968, Ser. No. 710,496

Int. Cl. B29h 5/00 U.S. Cl. 18-2 1 Claim ABSTRACT F THE DISCLOSURE A lubricating layer is fixed on the wall of the discharge orifice of a continuous internal mixer of the kind wherein the internal pressure of the material being mixed is controlled by the choking effect of this orifice on the material discharged therethrough whenever new material is fed into the mixer. This provides a smoother restraint of the discharging material and therefore more uniform control of the pressure on the material while it is in the mixer.

This invention relates to a continuous internal mixer of the kind disclosed by the E. H. Ahlefeld, Jr., et al. Pat. No. 3,154,808, dated Nov. 3, 1964, but its principles may be applied to any machine which discharges a stiff gel or a plastic material through a discharge orifice providing a back-pressure on material in the machine.

Using the Ahlefeld, Jr., et al. patent as an example, without purporting to thereby construe its scope, this patented mixer comprises a barrel forming two laterally interconnecting substantially cylindrical and mutually parallel chambers having at one end a common discharge orifice. Bladed rotors are located in these chambers and means are provided for receiving the material to be mixed and stuffing it under pressure into the chambers at a location spaced from the discharge orifice. Each of the rotors has a blade with a cross-section which is substantially like that of a Banbury-type blade and having a portion that twists away from its direction of rotation and a portion that twists in the opposite direction, the length and twist ratio between these oppositely twisting portions of the blade being such that when the chambers contain the material being mixed the average of the axially directed forces applied to the material by the blades of the rotors is insufficient to force the material through the orifice.

Therefore, the over-all axial travel of the material through the mixers chambers is dependent on the rate on which it is received by the means which stuffs the material under pressure into these chambers.

The discharge orifice opens transversely from the chambers in overlapped relation with respect to the rotors blades adjacent thereto. The rotors rotate in opposite directions such that these blade portions move towards the orifice and stuff the mixed material through the latter which is located centrally. across the junctions of the chambers. Preferably, the orifice has a width that is substantially greater than its depth so that the effective length of the active mixing zone of the mixer is as long as possible for any given over-all length.

The orifice is provided with walls of substantial length relative to the orifices cross-sectional area and which extend transversely from the rotors to form what is substantially a rectangular tube long enough to cause substantially increased resistance to the material discharging through the orifice. In other words, the passage of the material through the orifice is restrained frictionally because the material must be forced out while in contact with these walls.

Now this frictional restraint of the discharging material puts the material being mixed by the rotors under pressure as new material is continuously fed to the means which stuffs the material under pressure into the chambers at the location spaced from the discharge orifice. Control of this pressure is eected by making one of the orifice walls movable so that its spacing from the opposite orifice wall may be varied to thereby vary the discharge restraint on the material; that is to say, the choking effect on the discharged material can be varied.

Now, this restraint or choking action on the discharge material has not been accomplished as smoothly as is desirable in the direction of perfection. It is satisfactory but not perfect. Although frictional restraint is required, it should be smoothly achieved, but the restraint or choking effect actually achieved is somewhat rough, and for any given setting of the movable wall, for example, is somewhat variable when it should be of constant value.

The object of the present invention is to apply a more uniform or constant frictional restraint or back-pressure on the material discharged through the orifice of the described mixer or other machine.

With the above in mind, the present invention comprises a layer on the walls of the discharge orifice of the described mixer of an anti-friction material. This material should be something that is firmly fixed on the orifices Walls and can resist the relatively heavy shear to which it is subjected by its contact with the discharging material. At the same time, the material comprising the anti-friction layer should be such that under the heavy pressure applied to it by the discharging material, usually under elevated temperatures, its surface in contact with this material tends to ow at least slightly as required for lubricating action. With these properties, the lubricating layer on the discharge orifices walls causes the necessary frictional resistance of the discharging material to prevail but while being relatively free from roughness or what might be described as being an undesirable action somewhat like the chattering action that occurs between unlubricated relatively sliding metal surfaces, such as isfamiliar to those skilled in the bearing art.

One example of a material that may be used for the lubricating layer is the uorinated ethylene-propylene resin sold under the well-known trademark Teflon by E. I. du Pont de Nemours Co. This may be sprayed on the orifices walls or sheets of the material may be applied by a suitable adhesive. Preferably, a thin layer is sprayed on thewalls and allowed to set after which a second layer is sprayed and so on until the lubricating layer on the walls is adequately thick. The thickness required depends on the service life desired. When sheets of this material are used and are of adequate thickness possibly reinforced by ber glass, they may be mechanically applied to the orifices walls as by means of dove-tailed joining or the like.

Another lubricating layer that may be applied to the orifices walls is aluminum having a hard anodized surface with which the discharging mixed material contacts. Such a surface is non-metallic, resists shear to a high degree and yet has the characteristic of at least slight surface flow Iwhen subjected to the pressures encountered when restraining or choking the iiow of material discharging through the mixers orifice.

In general, any material providing a non-metallic surface for engagement by the discharging material With this surface capable of slight flow and with the material forming this surface adequately resistant to shear, may be used. Metallic materials, such as chrome plating or highly polished steel do not have this property.

A specific example of the present invention is illustrated by the accompanying drawings in which:

FIG. 1 is a vertical longitudinal cross-section of the discharge end of the described kind of machine, this section showing only the far cylindrical chamber of the barrel and its rotor but it being understood that the unillustrated cylindrical chamber and rotor are substantially the same as those illustrated; and

FIG. 2 which is a perspective view showing details of the discharge orifice assembly.

In these drawings, FIG. 1 is substantially the same as FIG. 4 of the drawings of the previously identified Ahlefeld, Ir., et al. patent, and FIG. 2 is substantially the same as FIG. 7 of the drawings of that patent.

The two figures are sufficient to show the barrel 1 which forms the two laterally interconnecting substantially cylindrical and mutually parallel chambers of which only the one far chamber 2 is shown. The common discharge orifice is shown at 3 it comprising the assembly shown by FIG. 2 and which is located in an opening 4 formed in the back or discharge end of the barrel 1, where the assembly is retained by a set screw 5. Each of the barrels contains a bladed rotor of which only the far one 6 is shown by the cross-section of FIG. 1. Each rotor has a blade 7 of the previously described cross-section with the previously described portions. To move material through the machine, it is necessary to stuff it under pressure into the unillustrated front or charging end of the machine, and as material is thus introduced, the mixed material is forced to be under pressure to stuff through the orifice 4, because of the latters previously described dimensional characteristics and, of course, depending on the adjustment of the swinging `wall 4a. The material can exit only by being forced through the orifice 4 because the back of each rotor has a shoulder 8 which blocks the material against axial discharge through the ends of the barrels chambers.

The previously described lubricating layer is shown in cross-section at 9 and it is to be understood that all four walls of the rectangular orifice have this lubricating layer of material on them. The characteristics of this lubricating layer have been described hereinbefore and need not be described now.

In general, it is to be understood that in a machine which forces a stiff gel or plastic material through a throttling or choking orifice for the purpose of resisting the flow of such material, may benefit from the present invention when the orifice is formed by a wall or walls of substantial length which frictionally resist the flow of the material. It is of course particularly useful in the case of a continuous mixer of the type disclosed by the previously mentioned Ahlefeld, Jr., et al. patent and insofar as is known, the machine of this patent is the only one wherein the internal pressure of the mixer is controlled in this fashion. However, there may be other instances where a stiff gel or plastic flow should be restrained to exert back pressure for other purposes.

In addition to the materials previously indicated as being suitable for the lubricating layer, the following are suggested as also being suitable:

Nylon Nylon with glass or powdered metal reinforcement Teflon with glass or powdered metal reinforcement Ceramics Polycarbonates (with some Teflon) Acetals (with some Teflon) Phenolics (Teflon with glass fillers) What is claimed is:

1. A machine which discharges a stiff gel or plastic material and having a discharge orifice therefore formed by a plurality of walls of substantial length relative to the orifices cross-sectional area and over which the material flows while in pressure contact therewith to be thereby frictionally restrained to exert a back pressure 0n the material, at least one wall thereof providing a tapered entry into said discharge orifice and another wall thereof being pivotable to allow changing said orifice opening; wherein the improvement comprises a layer of lubricating material fixed to each of said Iwalls along the entire interior lengths thereof including said tapered entry wall and said pivotable wall and which layer is resistant to the shear applied by the discharging material while having the property of at least slight surface flow under the pressure of the discharging material to provide a lubricating effect smoothing the friction restraint of the material,

said lubricating material consisting essentially of a plurality of thin sheets of fluorinated ethylene-propylene resin including therein a quantity of reinforcing fiber glass, said sheets being applied to said orifice walls by means of dove-tailed joints.

References Cited UNITED STATES PATENTS 2,604,662 7/1952 Bodkin. 2,799,045 7/ 1957 Hillegas. 3,154,804 11/1964 Ahlefeld et al 18-2 3,349,432 10/ 1967 Breneman 18-2 WILLIAM S. LAWSON, Primary Examiner 

